THE STORY OF AN ENTOMOLOGIST 



of sprays and spraying machinery. But the result of Pergande's 

 work completely negatived the necessity of sprays on the hop 

 crop. And this was the first experience that started in my mind 

 the idea that while sprays are of temporary value, that value lasts 

 only until the entomologist is able by his life history studies to 

 find something cheaper and easier and more natural, which will 

 bring about a more perfect control. In other words, while we 

 welcome the activity of the spray machine manufacturers, at 

 least temporarily, are we really not trying to put them out of 

 business.? 



The result of all the work here was to show that the plum is 

 the necessary secondary host of the plant-louse. The plum, of 

 course, is a perennial, while the hop vine is an annual. The 

 winter eggs of the plant-louse are laid upon the plum in the 

 autumn. In the spring they hatch, and there comes forth a gen- 

 eration of wingless virgin females but no males. These females 

 are called the stem mothers. They give birth to living young that 

 feed upon the sap of the plum leaves. Growth is very rapid and 

 there soon develops a generation of virgin females that are 

 winged. By that time the hop crop has been planted, and all of 

 this new winged generation fly to the hop (deserting the plum) 

 and give birth parthenogenetically to successive generations of 

 wingless females, all feeding upon the hop leaves and frequently 

 blighting the crop. Then, about the time of hop-picking, a 

 winged generation (all females) comes forth and flies back to 

 the plum trees. From these there comes a generation composed 

 of both males and females, and from this generation comes the 

 winter egg on the plum. What an extraordinary thing! The 

 removal of all plum trees near the hop yard or the destruction 

 of the lice on the plum in the spring by means of sprays perhaps 

 will free the ensuing hop yard from all possible danger from 

 this source. 



[73] 



